Optical navigation systems operate to estimate movements between the optical navigation systems and target surfaces to perform tracking operations. An optical navigation system uses a light source, such as a light-emitting diode (LED) or a laser diode, and an image sensor to successively capture frames of image data of a target surface. The optical navigation system compares the successive image frames and estimates the relative movements between the optical navigation system and the target surface based on the comparison between the current image frame and a previous image frame. The comparison is based on detecting and computing displacements of features in the captured frames of image data. For laser-based navigation systems, these features are usually interference images produced by a laser spot impinging on the target surface.
Optical navigation systems are commonly used in optical computer mice to track the movements of the mice relative to the surfaces on which the mice are manually manipulated. In order to perform the tracking operation properly, an optical mouse needs to be on the target surface since errors are introduced when the distance between the image sensor of the optical navigation system and the target surface is significantly increased, i.e., when the optical mouse has been lifted from the target surface. In an optical mouse with a laser-based navigation system, the optical interference images used for motion estimation grow as the distance between the image sensor of the system and the target surface is increased. Consequently, the navigation system can still be responsive after the optical mouse has been lifted from the target surface, which means erroneous motion estimates will be made by the navigation system.
The optical characteristics of the interference images do not allow a meaningful solution to the issue of lift detection using the image sensor of the optical navigation system. Thus, a separate sensing mechanism such as a mechanical switch is needed to detect when the optical mouse is lifted from a target surface.
Although conventional lift detection mechanisms work well for their intended purpose, there is a need for a non-complex and low cost lift detection mechanism for use in optical navigation systems.